Hi all, I have a 2 ton engine hoist that has a chain that is attached to the boom. The chain is secured by having a grade 8.8 metric bolt pass through its first link.My question is can I replace the bolt with a grade 9 imperial bolt ? I read that the metric 8.8 is the equivalent of a grade 5 , but am wary .

you ask a question that needs more information supplied to answer.Is the bolt used in 'tension' or 'shear'? Tension is end to end load,from the cap of the bolt,along its length to the nut.Shear is applied on the diameter of the bolt shank itself,where the diameter of the bolt body,along with its hardness(depending on application)will determine its capacity.Capacity will also depend on how its being loaded,slow steady application of load or weight may not break it;-but if u shock load it(like suddenly lowering a load on the hoist,then stopping it suddenly)-may fracture any fastener or bolt.From your question it sounds like the bolt is loaded in 'shear'.Is the chain supported on one side or both?(ie:does the chain have a support bracket(that its bolted to)-on both sides of the chain or just one side? If its just one you have a combination load-shear and tension.If the bolt is bolted thru a bracket on each side of the chain then you have a shear load.My solution would be to use the biggest diameter bolt in grade 5 that you can get thru the chain.Grade 5 will deform and bend before it snaps-giving you a chance to lower it and make safe.Use a grade 8/9 and it may snap suddenly.What size chain is being used and what do you plan to lift with it? Don't rely on cheap hardware anywhere else on the hoist-its only a strong as its weakest point.By the way,welcome to MBN..have fun and be safe

I would stay away from the higher tensile strength hardware as I would much rather the bolt bend a bit than snap a lot. The most common mistake with high tensile bolts is that they have a larger radius leading from the shank to the head and if the hole they are installed in hasn't been chamfered properly it will ride all the load in one spot telling the bolt to "break here". Only use those high priced bolts in places that need them. Welcome to the group! Terry